This invention relates to a differential apparatus having radially arranged pinion shafts rotatably supporting pinions disposed between and meshing with a pair of side gears.
This kind of differential apparatus, having radially arranged pinion shafts rotatably supporting pinions disposed between and meshing with a pair of side gears, is often used as a differential apparatus for a vehicle, since it is simple in construction and inexpensive. This kind of differential apparatus performs differential actions by bevel tooth engagement between a pair of side gears and pinions. Further, this kind of differential apparatus may perform the function of stopping those differential actions (differential lock: dif. lock) (see, for example, JP-A-10-096461), or stopping the transmission of power (cutting off power in a free running differential).
An example of a differential lock mechanism as disclosed in JP-A-10-096461 is described briefly with reference to FIG. 5C and FIG. 5D. The related differential apparatus includes a differential case 21, pinion shafts 27, pinions 41, side gears 43 and 45, a drive cam 25 disposed beside the side gear 45. The drive cam 25 has a dog clutch 31 between the side gear 45 and itself, and a pressing member 69 located inwardly of the outer periphery of the differential case 21 and adapted to press the drive cam 25 into movement upon operation of an actuator 65. In the related differential apparatus, a switch 55 engages the lower plate 51 of the actuator 65 for detecting a switchover in differential action of the actuator 65.
According to the related differential apparatus constructed as described in the above, a driving power from an engine is transmitted to the differential case 21, is differentially distributed to the side gears 43 and 45 through the pinion shafts 27 and the pinions 41 rotatably supported on the pinion shafts 27 and is transmitted to the right and left driving wheels (not shown). In the event that any excessive differential action is likely to occur from the wheel-spin of only one of the wheels, etc. when the vehicle has entered a bad road as in a muddy place, the actuator 65 is operated to cause the pressing member 69 to move the drive cam 25 axially to engage the dog clutch 31 to unite the side gear 45 and the differential case 21 into a differential lock, so that the vehicle may be able to leave the bad road.
In this related differential apparatus as described in the above, the pinion shafts 27 on which the four pinions 41 are rotatably supported, respectively, are usually mounted in a radial array in the differential case 21, as shown in FIG. 5A and FIG. 5B. The radial pinion shafts 27 comprise a diametrically disposed long pinion shaft 27A and short pinion shafts 27B disposed by a ring-shaped thrust block 28 at right angles to the long pinion shaft 27A. In order to dispose the short pinion shafts 27B at right angles to the long pinion shaft 27A, the related pinion shaft mounting structure has relied upon the aligning function of the thrust block 28, as in the case of the example shown. That is, the long pinion shaft 27A is mounted penetrating through a shaft hole 28A of the thrust block 28, and the short pinion shafts 27B are mounted penetrating through shaft holes 28B, the shaft holes 28B are perpendicular to the shaft hole 28A.
In the pinion shaft mounting structure employing the thrust block 28 as described, however, a stringent requirement for fitting accuracy has been made of the pinion shaft holes 28A and 28B in the thrust block 28. If fitting accuracy is low-between the pinion shaft holes 28A and 28B in the thrust block 28 and the pinion shafts 27, the short pinion shaft 27B is not definitely positioned in the pinion shaft hole 28B. Moreover, it is necessary for a high fitting accuracy to exist between the long pinion shaft 27A and the pinion shaft hole 28A in order to fix the thrust block 28 in position.
Further, it has been likely that the torque transmitted from the teeth of the dog clutch 31 may not be uniformly borne by the four pinion shafts, but may sometimes be borne by the long pinion shaft 27 alone, depending on the fitting accuracy between the pinion shaft holes 28A and 28B in the thrust block 28 and the pinion shafts 27A and 27B. In particular, an error is likely to be enlarged, since the positions of the pinion shaft holes 28A and 28B in the thrust block 28 are relatively far from the rotational axis, as shown in the drawing. Therefore, while a high working accuracy of the pinion shaft holes is required to avoid any uneven transmission of a load to the teeth on the dog clutch 31, the expensive and complicated heat treatment of the whole teeth or the selection of a material with high strength is required for coping with an uneven high load.
As a result, process steps are increased and extra parts are required for the thrust block, in addition, a freedom in the selection of materials is reduced.